In recent years, there is an increasing number of cyber attacks aiming at stealing information. Such cyber attacks include targeted email attack using emails, for example. Such a targeted email attack uses an email of which the From field and the body text are spoofed to make it look like one from a friend, for example.
A technique as follows has been used as a countermeasure against attacks from unauthorized users such as targeted emails as described above. For example, when a user accesses a server by operating a terminal connected to the network, the user is requested to input an ID (identification) and a password so as to obtain habitual information such as, for example, the average keyboard typing speed when inputting the ID and the password. Then, the obtained habitual information, in addition to the ID and the password, is compared with pre-registered habitual information of an authorized user, so as to detect an access from an unauthorized user. There is also a technique where, for example, the sender attaches a speech feature pattern obtained by uttering a password to an electronic mail, and the receiver of the electronic mail compares the speech feature pattern with a pre-received reference speech feature pattern of the sender himself/herself so as to determine if the sender is authentic.
Patent Document 1: Japanese Laid-open Patent Publication No. 2009-175984, and Patent Document 2: Japanese Laid-open Patent Publication No. 2000-172296 are introduced as the Related Art Document.
With the related techniques, however, a user has to take a special action, such as to input an ID and a password, or to utter a password, thereby increasing the burden on the user.